Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$56.84	3.290%	$58.71	$58.71	$58.70	$58.70
Purchase #2	$164.82	3.860%	$171.1821	$171.18	$171.20	$171.20
Purchase #3	$224.68	7.846%	$242.3084	$242.31	$242.30	$242.30
Purchase #4	$154.86	12.249%	$173.8288	$173.83	$173.85	$173.80
Purchase #5	$59.92	10.547%	$66.2398	$66.24	$66.25	$66.20
Purchase #6	$164.52	10.728%	$182.1697	$182.17	$182.15	$182.20
Purchase #7	$91.40	10.401%	$100.9065	$100.91	$100.90	$100.90
7 purchase totals =	$917.04		$995.3453	$995.35	$995.35	$995.30